Verizon Wireless and AT&T have both talked up their impending voice-over LTE (VoLTE) launches and how important it is to get the 4G voice technology exactly right first, but they haven't actually said what all their flavors of VoLTE will entail.

At its simplest form, VoLTE just needs to be voice and SMS to be on par with its circuit-switched predecessor. But, the beauty of being an all-IP technology means it can also include a full suite of rich communications services like IM, video chat, HD voice, presence and group chats.

Doug Makishima, COO of D2 Technologies, which provides embedded IMS software to LTE modem and chipset vendors and handset makers, as well as works with a whole host of operators on 4G voice, says the big two operators' strategies for VoLTE deployments will vary.

One is planning to roll out a complete RCS platform, while the other is going to just launch voice and text and iteratively add features on to it. Ever the gentleman, he wouldn't say which strategy went with which.

"One of the two will do a soft launch of VoLTE and then roll out more features later, so they might not make a whole lot of news around the first wave of VoLTE phones," Makishima says. "It'll be normal voice and SMS. On the other hand, we're hearing the other guy wants to have all these new features all together, and that's the advantage of [VoLTE]."

Both AT&T and Verizon say they are getting close to deployment. Verizon reiterated Thursday in its earnings that it would start testing and launch its first VoLTE handsets sometime this year, with a commercial launch next year, while AT&T has said it will go live this year. Makishima says he's more confident that the operators won't push back their launch dates now than ever before. (See Verizon Ups Spend for VoLTE & 4G Video Hogs and AT&T Plans 4G Voice Launch This Year.)

When VoLTE does go live, consumers might not care how robust the voice service is on day one. Most already have their own preferred video and IM clients. And, if operators introduce new free services that improve their voice calling, that would just be a bonus. What they will care about is that their 4G voice service works as well, if not better, than what they are used to.

The wireless operators get this. That's why VoLTE has had several delays and setbacks. They're going to get it right on day one. But, just like a "market" covered with LTE means different things to different operators, just how advanced each VoLTE service is will likely vary as well.

— Sarah Reedy, Senior Editor, Light Reading